Surgical resection of secondary liver tumors has been shown to be an effective treatment in some patients with five year survival between 20-30 percent. Unfortunately, the surgery has a relatively high complication rate with 35 percent of patients suffering minor complications. About 15 percent suffer more serious complications with a mortality rate of 2-5 percent. In addition the average hospital stay is about two weeks without complications. Deep noninvasive coagulation of liver tumors could potentially eliminate some of these disadvantages of liver surgery. Most notably it could be feasible to eliminate infections and perform the procedure with short or no hospital stay. This could translate in to large cost savings and perhaps extend the therapy to patients who would not be eligible for major surgery due to other health reasons. During the current grant period we developed ultrasound phased array systems, and magnetic resonance temperature monitoring techniques that could be used for liver surgery. We have developed a 512 channel driving system for the phased arrays, theoretically designed and experimentally tested different array configurations, and developed array manufacturing techniques for magnetic resonance (MR) scanner compatible large scale arrays. We constructed a large scale array to demonstrate the feasibility of the proposed technique. Finally, we have shown that the temperature elevation induced during high power sonications in tissue can be quantified using MR temperature imaging. Now we propose to use our experience and hardware for the development of a noninvasive surgery technique for clinical liver tumor treatments. To reach this goal several basic ultrasound arrays and beam propagation concepts still need to be investigated prior to our ability to accurately execute noninvasive liver surgery. These will include theoretically optimizing the large scale array design for liver treatments, testing the designed arrays, and developing and testing ultrasound propagation models that take into account nonlinear propagation, tissue temperature elevation, and tissue changes due to thermal exposures. These theoretical models are required for accurate multi focal pattern sonication planning and control of the treatments. In addition the procedures for clinical liver treatments need to be developed and tested. Finally, we plan to investigate the potential of using ultrasound induced vascular occlusion for cancer therapy. In conclusion, during the current grant period we developed the basic tools that will make accurate noninvasive coagulation of liver tumors possible. During the next phase of this grant we plan to complete all of the required research so that the therapy can be tested in clinical treatments. The noninvasive focused ultrasound coagulation of liver tumors has a large clinical potential in reducing complication rates and costs associated with open surgery.